chapter 17 KNES a
exercise (heat) exhaustion signs and symptoms
*thirst, headache, dizziness, light-headedness, mild anxiety, fatigue, profuse sweating, weak and rapid pulse, and low blood pressure in the upright position are common signs and symptoms;* the individual may appear to be *ashen and gray, with cool, clammy skin*; an uncoordinated gait is often present; sweating may be reduced if the person is dehydrated, but body temperature generally does not exceed 39.5 C (103 F); the individual hay have an urge to defecate or experience diarrhea; significant neurological impairment is absent 329
weight charts
- Pre- and postpractice weigh-in - 1% loss—significant increase in rectal temperature - 4%-5%—impairment in work capacity, physiologic function, and thermoregulation - Fluid must be replaced before return to practice is permitted
heat syncope or orthostatic dizziness
Collapsing in the heat, resulting in loss of consciousness Standing erect in a hot environment, causing postural pooling of blood in the legs Lay patient supine and elevate legs to restore central blood volume recovery often occurs within hours
electrolyte replacement
Electrolytes • Sodium, chloride, magnesium, and potassium • Regulate fluid balance, nerve conduction, and muscle contractions - Sweat contains high levels of sodium and chloride - Replaced with normal diet - Use of electrolyte drinks - Avoid diuretics
clothing
Light-colored, lightweight, porous clothing - Least amount of clothing appropriate to the sport - Be aware of problems that can be caused by equipment (e.g., FH goalie)
heat syncope or orthostatic dizziness
Management • Supine position; legs above the level of head • Monitor vital signs • Replace any water deficit
relative humidity
SLIDE INFO Relative humidity - Ratio of water in the ambient air to the total quantity of moisture that can be carried • When humidity is high, evaporation will be slow; minimal water is accepted into the air Sweating continues but evaporation is slight; could result in a substantial fluid loss—up to 2.5 L/hr (6 lbs) Excessive fluid loss without replacement → dehydration slide 4
heat syncope or orthostatic dizziness
Signs and symptoms • Dizziness • Low blood pressure • Blurred or tunnel vision • Pale or sweaty skin • Weakness or fatigue • Reduced pulse rate • Elevated skin temperature
fluid rehydration
*thirst is not an adequate indicator of water needs during exercise; * physically active individuals may not become thirsty until systemic water loss equals 2% of body weight; rather, thirst develops in response to increases in osmolarity and blood sodium concentrations and decreases in plasma volume caused by dehydration 324
exercise (heat) exhaustion management
__________________: elevating the legs to reduce postural hypotension can also be effective; if recovery is not rapid and uneventful, *the individual should be transported to the closest medical facility;* intravenous fluids may need to be administered; some individuals, particularly endurance athletes exercising in the heat, may require as much as 4 L of fluid replacement; physical activity should not be resumed until the individual has returned to the pre-dehydrated state and been cleared by a physician 329
exertional heat stroke management
__________________: the emergency plan, including *summoning emergency medical services (EMS), should be activated*; mortality and organ damage appear to be directly proportional to length of time between elevation of core body temperature and initiation of cooling therapy; as such, while waiting for EMS to arrive, the *individual should be moved immediately to a cool place; all equipment and unnecessary clothing should be removed, and rapid cooling of the body should be initiated; * physical activity should not be resumed until the individual has returned to the pre-dehydrated state and been cleared by a physician 330
heat illnesses
if the signs and symptoms of heat stress (E.g. thirst, fatigue, lethargy, flushed skin, headache, and visual disturbances) are not treated, cardiovascular compensation begins to fail, and a series of progressive complications termed ___________________, can result; the various forms of ________________, in order of severity, include exercise-associated muscle (heat) cramps, exercise (heat) exhaustion, and exertional heat stroke; although symptoms often overlap between the conditions, failure to take immediate action can result in severe dehydration and possible death 327
weight charts
measuring *pre- and post-exercise weight* can decrease the risk of heat illness; a fluid loss equivalent to as little as *1% of body mass is associated with a significant increase in rectal temperature*; for each liter of sweat-loss dehydration, the heart rate can increase by approximately eight beats per minute, with a corresponding decrease in cardiac output; when water loss reaches *4 to 5% of body mass, a definite impairment is noted in physical work capacity, physiologic function, and thermoregulation*; a rule of thumb is that for every pound of water lost, 24 oz (i.e. three cups) of fluid should be ingested, meaning that 150% of the fluid loss during exercise is replenished 327
practice schedules
on hot, humid days, workouts, practices, and competitions should be scheduled during *early morning or evening hours to avoid the worst heat of the day (i.e. 11:00 AM to 3:00 PM)*; it also may be necessary to *allow frequent water breaks (i.e. 10 minutes every half an hour)*, shorten practices, and lessen the exercise intensity; whenever possible, participants should be moved out of direct sunlight (e.g. shade trees and tents), and restrictive equipment (e.g. pads and helmets) should be removed frequently 327
tolerance to heat
several factors can affect an individual's _______________________; acclimatization and proper hydration are among the most critical in preventing heat illness 324
fluid rehydration
several steps can be taken to ensure adequate ___________________ before, during, and after exercise; in order to prevent dehydration, fluids must be ingested and absorbed by the body; running through sprinklers or pouring water over the head may feel cool and satisfying, but it does not prevent dehydration; *a standard rule is to drink until thirst is quenched- and then drunk a few more ounces* 325
exertional heat stroke management
When EHS is suspected, the patient's body (trunk and extremities) should be quickly immersed in a pool or tub of cold water. Removing excess clothing and equipment will enhance cooling by maximizing the surface area of the skin. However, because removing excess clothing and equipment can be time consuming, CWI should begin immediately and equipment should be removed while the patient is in the tub (or while temperature is being assessed or the tub is being prepared).59 Rectal temperature and other vital signs should be monitored during cooling every 5 to 10 minutes if a continuous monitoring device is not available. Cold-water immersion up to the neck is the most effective cooling modality for patients with EHS. The water should be approximately 1.7C (35F) to 15C (59F) and stirred continuously to maximize cooling. The patient should be removed when core body temperature reaches 38.9C (102F) to prevent overcooling If full-body CWI is not available, partial-body immersion (ie, torso) with a small pool or tub and other modalities, such as wet ice towels rotated and placed over the entire body or cold-water dousing with or without fanning, may be used but are not as effective as CWI
exercise (heat) exhaustion signs and symptoms
______________ include: dizzy headache profuse sweating rapid, shallow breathing cool, clammy skin ashen or gray skin body temperature or slightly elevated rapid, weak pulse uncoordinated gait 329
exercises associated muscle (heat) cramps
_______________ are painful, *involuntary muscle spasms caused by excessive water and electrolyte loss* during and after intense exercise in the heat; paradoxically, the condition most frequently occurs in well-conditioned, acclimatized, physically active individuals who have overexerted themselves in hot weather and rehydrated only with water; predisposing factors include lack of acclimatization, use of diuretics or laxatives, and sodium depletion in the normal diet; the condition can be prevented by ingesting copious amounts of water and increasing the daily intake of salt through a normal diet several days before the period of heat stress 327
children
_______________ have a lower sweating capacity and higher core temperature during exposure to heat as compared to adolescents and adults; this occurs even though ______________ have a higher number of heat-activated sweat glands per unit of skin; sweat composition in ______________ also differs; children excrete higher concentrations of sodium and chlorine and lower concentrations of lactate and potassium; *therefore, ______________ do not benefit from electrolyte beverages and should use only cool water for fluid replacement;* *in addition, children require a longer time to acclimatize to heat as compared to adolescents and young adults* 326
hyperthermia
_______________, or elevated body temperature, occurs when internal heat production exceeds external heat loss; the hypothalamus is a gland that maintains homeostasis, or a state of equilibrium within the body, by initiating cooling or heat-retention mechanisms to achieve a relatively constant body core temperature between 36.1 and 37.8 C (97-100 F); *the body core encompasses the skull, thoracic, and abdominal area* 322
physiologic changes seen after 10 days of heat exposure
________________ include: heart rate and body temperature decrease peripheral blood flow and plasma volume increase sweating capacity nearly doubles sweat becomes more diluted (i.e. less salt is lost) sweat is distributed more evenly over the skin surface the increased perspiration rate is sustained over a longer period of time 324
exercise (heat) exhaustion management
________________: the individual should be *moved immediately to a cool place; all equipment and unnecessary clothing should be removed; rapid cooling of the body should be initiated; * two effective cooling methods are evaporative cooling and ice immersion; evaporative cooling involves spraying copious amounts of tap water over the individual's skin with air fanning; ice immersion involves placing the individual into a pool or tube of cold water (~1 to 15 C; 35 to 59 F); circulation of the water may enhance cooling; if immersion in ice water is not available, other cooling methods should be used; these may include wrapping in cool, wet, iced towels; using fans; and applying crushed-ice packs to the neck, axilla, and groin; fans and cool-mist machines, however, have limited use during humid conditions; it is essential to administer copious amounts of cool fluids with a diluted electrolyte solution as quickly as possible 329
environmental conditions
_________________ affect even the best conditioned individuals; participation in physical activity on hot, humid days or on cold, windy days predisposes individuals to hyperthermia and hypothermia, respectively; in addition, exercising during thunderstorms that produce lightning can be extremely dangerous 332
evaporation
_________________: *the most effective heat-loss mechanism used to cool the body;* sweat evaporates when molecules in the water absorb heat from the environment and become energetic enough to escape as a gas; as core temperature rises during exercise or illness, peripheral blood vessels dilate and sweat glands are stimulated to produce noticeable sweat, which can amount to a loss of 1.5 to 2.5 liters of body water in 1 hour; on a hot, dry day, sweating is responsible for more than 80% of heat loss; the total sweat vaporized from the skin depends on three factors: the skin surface exposed to the environment the temperature and relative humidity of the ambient air the convective air currents around the body 323
healthy individuals at risk for heat illness
_________________: include those who are poorly acclimated or conditioned, those who are inexperienced with heat illness, those with large muscle mass, children, wheelchair athletes, Special Olympians, and elderly people, previous history of heat illness (added) 327
radiation
_________________: the loss of heat from a warmer object to a cooler object in the form of infrared waves (thermal energy) without physical contact; for example, when temperatures of surrounding objects in the environment, such as the sun or hot artificial turf, exceed skin temperature, radiant heat is absorbed by the body 323
electrolyte replacement
___________________ *solutions are unnecessary for individuals with normal diets; *individuals demanding peak performance in competitions of greater than 1 hour or during intense intermittent exercise, however, may benefit from carbohydrate drinks; commercial drinks may be used but should be cooler than ambient temperature (10 to 15 C, 50 to 59 F), flavored to enhance palatability, range between 4 to 8% of multiple transportable carbohydrate, and contain a small amount of sodium chloride; _____________ drinks should be consumed during the pre-exercise hydration session (2 to three hours pre-exercise) and 30 minutes before exercise; during exercise, 1 L of a 6% carbohydrate drink is recommended every hour; fruit juices, carbohydrate gels, sodas, and some sports drinks have carbohydrate concentrations of greater than 8% and are not recommended during an exercise session as the sole beverage; while maintaining hydration, the participant should avoid *diuretics, such as excessive amounts of protein, caffeinated drinks (e.g. soda, tea, coffee), chocolate, and alcoholic beverages* 326
exercises associated muscle (heat) cramps signs and symptoms
___________________ commonly occur in the calf, hamstrings, and abdominal muscles, but they also may involve the muscles of the upper extremity; signs and symptoms mimic dehydration and include thirst, sweating, *transient muscle cramps, and fatigue; * *body temperature is not usually elevated, and the skin remains moist and cool; * *pulse and respiration may be normal or slightly elevated;* dizziness may be present 328
weight charts
___________________: in addition to fluids, carbohydrates should also be ingested within 30 minutes postexercise, especially those with high water content (e.g. melons or tomatoes); even under the best circumstances, 24 hours is needed to fully restore the fluids and muscle glycogen that are used during just 2 hours of strenuous exercise; before the next exercise period, the individual should ingest 3.5 to 4.5 g of carbohydrates per pound of body weight; alcohol should be avoided; *lost fluid should be replaced and weight normalized before the next episode of exercise* 327
exercises associated muscle (heat) cramps management
___________________: the coach should *require the individual to stop activity, provide fluids (if available, fluids containing sodium), and begin mild, passive stretching of the involved muscle(s) and ice massage over the affected area;* the individual should ingest enough fluids to drink beyond the point of satisfying thirst; a recumbent position may allow more rapid redistribution of blood flow to cramping leg muscles; the individual should be watched carefully, because this condition may precipitate heat exhaustion or heat stroke 328
conduction
___________________: the direct transfer of heat through a liquid, solid, or gas from a warm object to a cooler object; for example, a foot-ball player can absorb heat through the feet simply by standing on hot artificial turf 323
convection
___________________: transfer of heat depends on conduction from the skin to the water or air next to it; the effectiveness of heat loss depends on how fast the air (or water) next to the body is exchanged once it becomes warmer; if air movement is slow, air molecules next to the skin are warmed and act as insulation; in contrast, if warmer air molecules are continually replaced by cooler air molecules, as occurs on a breezy day or in a room with a fat, heat loss increases as the air currents carry heat away; in water, the body loses heat more rapidly by convection while swimming than while lying motionless 323
individuals at risk for heat illess
____________________ include: HEALTHY INDIVIDUALS -age extremes (children, elderly person) -excessive muscle mass, large, or obese -poorly acclimatized or conditioned -previous history of heat illness -salt or water depletion -sleep deprived INDIVIDUALS WITH ACUTE ILLNESS -illnesses that involve fever -gastrointestinal illnesses INDIVIDUALS WITH CHRONIC ILLNESSES -alcoholism and substance abuse (e.g. amphetamines, cocaine, hallucinogens, laxatives, diuretics, narcotics) -cardiac disease -certain nutritional supplements (e.g. creatinine phosphate) -cystic fibrosis -eating disorders -medications (e.g. anticholinergics, antidepressants, antihistamines, diuretics, neuroleptics, b-blockers) -skin problems with impaired sweating (e.g. millaria rubra or millaria profunda) -uncontrolled diabetes mellitus or hypertension -*using oil- or gel-based suscreens that block evaporative cooling* WHEELCHAIR ATHLETES -have a spinal cord injury (alters thermoregulation) -limit water intake to avoid going to the bathroom 328
exertional heat stroke signs and symptoms
____________________ include: disoriented unconscious initially profuse sweating; no sweat in later stages shallow breathing hot, dry skin reddish skin body temperature increased markedly rapid, strong pulse 329
heat gains and loss
____________________: heat produced within working muscles is transferred to the body's core and skin; during exercise, body heat is dissipated into the surrounding environment by radiation, conduction, convection, and evaporation 322
exertional heat stroke
_______________________ is the least common, but most serious, heat- related illness; in football, _______________ is second only to head injuries as the most frequent cause of death; the condition also is seen in dehydrated distance runners and wrestlers; ________________ almost always is preceded by prolonged, strenuous physical exercise in individuals who are poorly acclimatized or seen in situations during which evaporation of perspiration is blocked 330
exercise (heat) exhaustion
_______________________ usually occurs in unacclimatized individuals during the first few intense exercise sessions on a hot day; those who wear protective equipment or heavy uniforms are at greater risk, because evaporation through the material may be retarded; it is a functional illness and is not associated with organ damage; _________________ is caused by *ineffective circulatory adjustments compounded by a depletion of extracellular fluid, especially plasma volume, as a result of excessive sweating*; blood pools in the dilated peripheral vessels, which dramatically reduces the central blood volume necessary to maintain cardiac output 328
internal heat regulation
as exercise beings, heart rate and cardiac output increase, while superficial venous and arterial blood vessels dilate to divert warm blood to the skin surface; heat is dissipated when the warm blood flushes into skin capillaries; this is evident when the face becomes flushed and reddened on a hot day or after exercise; when the individual is in a resting state and the air temperature is less than 30.6 C (87 F), approximately two-thirds of the body's normal heat loss results from conduction, convection, and radiation; as air temperature approaches skin temperature and exceeds 30.6 C, evaporation becomes the predominant means of heat dissipation 322
relative humidity
_________________________ is the most important factor in determining the effectiveness of evaporative heat loss; _________________ is the ratio of water the the ambient air to the total quantity of moisture that can be carried in air at a particular ambient temperature; it is expressed as a percentage; for example, 65% ________________ means that ambient air contains 65% of the air's moisture-carrying capability as the specific temperature; when humidity is high, the ambient vapor pressure approaches that of the most skin, and evaporation is greatly reduced; therefore, this avenue for heat loss is closed, even though large quantities of sweat bead on the skin, eventually roll off; in this form, sweating represents a useless water loss that can lead to a dangerous state of dehydration and overheating; when temperature and _____________________ are combined, the values can be charted on the heat index to determine the risk of potential heat illness 323
fluid rehydration
an easy method to determine if enough fluids are being consumed is to monitor the color and volume of the urine; an average adult's urine amounts to 1.2 quarts in a 24-hour period; urination of a full bladder usually occurs four times each day; within 60 minutes of exercise, passing light-colored urine of normal to above-normal volume is a good indicator of adequate hydration; if the urine is dark yellow in color, of a small volume, and of strong odor, the individual needs to continue drinking; ingesting vitamin supplements often can result in dark-yellow urine; as such, urine color, volume, and odor must all be considered when determining hydration status 325
exertional heat stroke signs and symptoms
by definition, the condition occurs when body temperature is elevated to a level that causes characteristic clinical and pathological damage to body tissues and affects multiple organs; *initial symptoms include a feeling of burning up, confusion, disorientation, irrational behavior, agitation, profuse sweating, and an unsteady gait*; *as the condition deteriorates, sweating ceases; the skin is hot and dry and appears to be reddened or flushed; the individual hyperventilates or breathes deeply and has dilated pupils, giving the appearance of a glassy stare; * *as core temperature rises, the pulse becomes rapid and strong (as high as 150 to 170 beats per minute); the individual may become hysterical or delirious;* *tissue damage by excessive body heat leads to vasomotor collapse, shallow breathing, decreased blood pressure, and a rapid and weak pulse; * *muscle twitching, vomiting, or seizures may occur just before the individual lapses into a coma *330
exertional heat stroke
during exercise, metabolic heat continues to rise; decreased blood plasma volume causes the heart to beat faster and work harder to pump blood through the circulatory system; *the thermoregulatory system is overloaded, and the body's cooling mechanisms fail to dissipate the rising core temperature; * the hypothalamus shuts down all heat-control mechanisms, including the sweat glands in an effort to conserve water loss; a vicious circle is created in which, as temperature increases, the metabolic rate increases, which in turn increases heat production; the skin becomes hot and dry; as the temperature continues to rise, permanent brain damage may occur; core temperature can rise to 40.6 C (105 F), and it has been known to reach 41.7 to 42.2 C (107 to 108 F); if untreated, death is imminent; mortality is directly related to the magnitude and duration of the hyperthermia 330
internal heat regulation
during exercise, the circulatory system must deliver oxygen to the working muscles and heated blood from deep tissues (i.e. core) to the periphery (i.e. shell) for dissipation; the increased blood flow to the muscles and skin is made possibly by increasing cardiac output and redistributing regional blood flow (i.e. blood flow to the visceral organs is reduced) 322
internal heat regulation
during exercises, the body gains heat either from external sources (i.e. environmental temperatures) or from internal processes; much of the __________________ is generated during muscular activity through energy metabolism; the act of shivering can increase the total metabolic rate by three to five fold; during sustained, vigorous exercise, the metabolic rate can increase by 20 to 25 fold above the resting level; theoretically, such a rate can increase core temperature by approximately 1 C (1.8 F) every 5 to 7 minutes 322
acclimatization
exercising moderately during repeated heat exposures can result in physiologic adaption to a hot environment, which can improve performance and heat tolerance; in general, the major ________________ occurs during the first week of heat exposure and is complete after 10 to 14 days; only 2 to 4 hours of daily heat exposure is required; the first several exercise sessions should be light and last approximately 15 to 20 minutes; thereafter, exercise sessions can progressively increase in duration and intensity; well- ______________ individuals should train for 1 to 2 hours under the same heat conditions that will be present during their competitive event; proper hydration is essential for the _________________ process to be effective 324
strategies to reduce risk of dehydration
healthy population: drink 8 to 12 cups (8 oz/ cup) of fluid at least 24 hours before an event drink at least 16 oz of fluid 2 hours before exercise and again approximately 20 minutes before exercise when exercising for 1 hour or more, drink at least 5 to 10 oz of fluid every 15 to 20 minutes; drink beyond satisfying thirst drink cool fluids containing less than 8% carbohydrates use individual water bottles to accurately measure fluid consumption freeze fluid in plastic bottles before exercise; the bottles will thaw and stay cool during exercise sessions record pre- and post-exercise weight to determine if excessive and unsafe weight loss has occurred replenish lost fluid with at least 24 oz of fluid for every pound of body weight lost avoid caffeine, alcohol, and carbonated beverages *children (in addition to above): allow 10 to 14 days of acclimatization reduce intensity of prolonged exercise* 325
acclimatization
heat ___________________ is lost rapidly, however; as a general rule, 1 day of heat _______________ is lost over 2 to 3 days without heat exposure, with the major benefits being lost within 2 to 3 weeks after returning to a more temperate environment 324
basal level of body heat loss
in addition to heat loss through sweating, a _________________ exists because of the continuous evaporation of water from the lungs, from the mucosa of the mouth, and through the skin; this averages approximately 350 mL of water as it seeps through the skin every day, as well as another 300 mL of water vaporized from mucous membranes in the respiratory passages and mouth; the latter is illustrated when you see your breath in the very cold weather; in total, it is not uncommon for an individual to lose 1.5 to 2.5 L/hour of water during exercise; this translates to a loss of 3 to 6 pounds of body weight per hour; during a 2 to 3 hour workout, an individual could lose from 6 to 12 pounds of body weight; although an individual may continually drink water throughout an exercise bout, less than 50% of the fluid lost is replenished; this voluntary dehydration was recognized long ago and continues to be characterized by researchers; accordingly, a physically active individual should drink as much fluid as possible before exercise and before thirst is perceived during exercise; it is critical to drink beyond the perception of satisfying one's thirst to hyperhydrate the body to prevent voluntary dehydration 324
middle aged and older adults
in general, ___________________ are *less tolerant to exercising in heat;* when compared to younger men and women, ________________ develop higher heart rates, higher skin and core temperatures, and lower sweat rates during exercise in heat aging can lead to a limited peripheral vascular response that can impair local vasodilation; *onset of sweating also appears to be delayed* with advancing age, and the sweating response appears to be blunted; this may result from either a limitation in sweat gland output or a dehydration-limited sweat output if fluid replacement is insufficient; in addition, older individuals *do not recover from dehydration as effectively as younger individuals do,* which may be related to a blunted thirst drive; this may make older individuals more prone to dehydration that could adversely affect the thermoregulatory capacity 326
diuretics, supplements, and medications
individuals taking ____________- or laxatives should be carefully observed for dehydration; these agents *induce fluid loss, reduce plasma volume*, and may adversely affect thermoregulation and cardiovascular function; substances used to induce vomiting and diarrhea also leads to dehydration and may cause excessive electrolyte loss with accompanying muscle weakness; some nutritional supplements, such as creatine phosphate, require additional fluids to decrease the risk of heat cramps and other associated heat illnesses; medications, such as B-adrenergics, anticholinergis, antihistamines, B-blockers, calcium channel blockers, and tryclycic antidepressants can impair the body's normal mechanisms of dissipating heat, which may result in a dangerously high core temperature; before taking supplements or medications, an individual should be *FULLY INFORMED regarding the proper use and possible side-effects of the substances* 327
fluid rehydration
it is essential that physically active individuals begin an exercise session when they are well hydrated and have ready access to adequate water replacement throughout the exercise session to prevent dehydration; pre-exercise hydration should involve 17 to 20 oz of water or a sports drink 2 to 3 hours before exercise and 7 to 10 oz of water or a sports drink 10 to 20 minutes after exercise; cold liquids, especially water, empty from the stomach and small intestine significantly faster than warm fluids do; _________________ during exercise should approximate the losses of sweat and urine, resulting a loss of body weight no greater than 2% of weight; this generally requires 7 to 10 oz of fluid every 10 to 20 minutes; postexercise hydration should be completed within 2 hours of the exercise bout; this should include water, carbohydrates to replenish glycogen stores, and electrolytes to speed rehydration 324
clothing
light-colored, lightweight, porous ____________ is preferred to dark, heavyweight, nonporous material; ____________ made of 100% cotton is not recommended, especially in hot climates, because moisture in sweat-soaked cotton does not evaporate easily; evaporative heat loss occurs only when _____________ is thoroughly wet and perspiration can evaporate; changing into a dry shirt simply prolongs the time between sweating and cooling; heavy sweat suits or rubberized plastic suits produce high relative humidity close to the skin and retard evaporation, severely increasing the risk of heat illness; even when wearing only football helmets and loose-fitting porous jerseys and shorts, 50% of the body surface of football players can be sealed and evaporative cooling limited; the increased metabolic rate that is needed to carry the weight of the equipment and the increased temperature on artificial surfaces also can increase the risk of heat illness; as such, football players should initially practice in t-shirts, shorts, and low-cut socks; on hot, humid days, uniforms should not be worn, and if possible, shoulder pads and helmets should be removed often to allow radiation and evaporative cooling; because much of the body's heat escapes through the head, helmets used in noncontact sports (e.g. cycling) should allow adequate airflow and evaporation 326
sex
the general consensus is that *women can tolerate the physiologic and thermal stress of exercise at least as well as men of comparable fitness level and level of acclimatization*; both __________ can acclimatize to a similar degree; however, sweating does differ; although women possess more heat- activated sweat glands per unit of skin area as compared to men, *women sweat less than men do*; compared with men, women begin to sweat at higher skin and core temperatures, produce less sweat for a comparable heat-exercise load, yet show an equivalent heat tolerance; women probably rely more on circulatory mechanisms for heat dissipation, whereas men rely on evaporative cooling; *the production of less sweat to maintain thermal balance can provide women with significant protection from dehydration during exercise at a high ambient temperature* 326
electrolyte replacement
the minerals sodium, chloride, magnesium, and potassium are called electrolytes because they are dissolved in the body as electrically charged particles called ions; _____________ regulate fluid balance, nerve conduction, and muscle contractions; sweat contains high levels of sodium and chloride but little potassium, calcium, or magnesium; ionic concentrations in sweat are greatly influenced by the rate of perspiration and acclimatization; 4 L of perspiration equals an approximated 5.8 % loss of body weight; such a loss can lower the body's content of sodium and chloride by 5 to 7% and of potassium by less than 1.2 %; because the body loses more water than electrolytes, the ionic concentration of these minerals in the body fluids rises; *accordingly, during periods of heavy perspiration, the need to replace body water is greater than the need to replace electrolytes;* lost electrolytes are readily replenished by adding a slight amount of salt to food or by eating potassium-rich foods, such as citrus fruits and bananas; a glass of orange or tomato juice replaces almost all the potassium, calcium, and magnesium excreted in approximately 3L of sweat 325
fluid rehydration
the primary objective of ______________ is to maintain plasma volume so that circulation and sweating occur at optimal levels; dehydration progressively decreases plasma volume, peripheral blood flow, sweating, and stroke volume (i.e. the quantity of blood ejected with each heartbeat), and it leads to a compensatory increase in heart rate; the general deterioration in circulatory and thermoregulatory efficiency increases the risk of heat illness, impairs physiologic functions, and decreases physical performance 324
thermoregulation
the process by which the body maintains body temperature is called ___________________; it is controlled primarily by the hypothalamus, which is a region of the diencephalon forming the floor of the third ventricle of the brain 322
